<!DOCTYPE html>
<style>
.cb {
  position: relative;
  border: 3px solid black;
  height: 100px;
  width: 150px;
  display: inline-block;
  vertical-align: top;
  margin: 5px;
}
.abs {
  margin: 0;
  position: absolute;
  box-sizing: border-box;
  top: 3px;
  left: 3px;
  outline: 2px solid lime;
  width: calc(100% - 6px);
  height: calc(100% - 6px);
}
</style>
<div class="cb"><button class="abs">button</button></div>
